Diffuse scattering from large-angle, thermally induced, orientational disorder in molecular crystals

Area of Science:

• Solid-state physics
• Materials science
• Crystallography

Background:

• Scattering calculations often approximate molecular motion, neglecting large-angle rotations (librations).
• Accurate modeling of thermal disorder in molecular solids is crucial for understanding their properties.

Purpose of the Study:

• To develop and demonstrate a method for incorporating large-angle librations into scattering calculations.
• To analyze the impact of librational motion on thermal disorder scattering in molecular solids.

Main Methods:

• Treating molecules as independent librators in harmonic potentials using large-angle rotation mathematics.
• Applying a Gaussian probability distribution to smear the molecular form factor.
• Calculating molecular Fourier transforms and applying librational and translational smearing.

Main Results:

• Librational smearing significantly affects the molecular form factor, especially at larger scattering vectors.
• The influence of librations is largely insensitive to approximations in the calculation.
• The Debye-Waller effect of vibrations decreases with increasing scattering vector.

Conclusions:

• The developed method effectively models the influence of large-angle librations on scattering.
• Both librational and vibrational motions significantly modify molecular scattering patterns.
• This approach provides a clearer understanding of how molecular dynamics affect scattering data.